The subject matter of the application relates to a method and an apparatus for separating out printed products from a stack. The apparatus includes a pushing device for separating out the printed products and a downstream-arranged removal device for conveying away the separated out printed products.
For separating out printed products from a hopper, in particular perfect-bound printed products having a thickness starting at approximately 2 mm, so-called pusher-feeders are frequently used which comprise a pushing device and a downstream-installed removal device. With this type of technology, the separation capacity is limited owing to the relatively large mass which must be moved with a corresponding stroke of the pushing device. The speed jump experienced by the printed products during the transfer from the pushing device to the removal device, however, leaves unsightly markings on these printed products.
German patent document DE 1247266 provides an apparatus to convey away books and booklets from a filler hopper with the aid of a translational back and forth moving pusher. The pushing device, which makes contact in a form-fitting manner with the back side of the lowest book, comprises stopped conveying belts on the top, wherein this is intended to prevent smudging of the printed surface of the second-lowest book during the movement. The pushing device is moved with the aid of a rotating crank disk and, in the process, carries out an unchangeable sequence of movements. The accelerations which occur during the pushing of a printed product therefore cannot be optimized, which results in a disadvantage for separating apparatuses with a high rate of production.
The German patent document DE 9208033U1 discloses a device which is also provided with a back and forth moving feed element for separating out blanks made of cardboard, corrugated cardboard or the like. In the process, the feed element initially grips the lowest blank in a form-fitting manner, with the aid of transporters attached thereto, wherein following the lifting up of the feed element and thus also the transporters, the second to the lowest blank is also moved along with the aid of suction openings formed into the top of the transporters. While the third to the lowest blank rests against a rear end stop, the movement of the second to the lowest blank is stopped at a front end stop, and the lowest blank to be separated out is conveyed further through an opening to a downstream-arranged machine. The separating of the blanks thus occurs in a two-phase process which is intended to improve the operational safety. Prior to the return movement of the advancing element, however, this element along with the transporters must again be lowered to its starting position. In the process, the feed element realizes a large stroke in pushing direction, as well as at a right angle thereto, which requires comparatively expensive mechanical elements and has a negative effect on the production costs and the service life, as well as the achievable output rate.
The German patent document DE 19756374A1 discloses an apparatus for separating out book covers from a stack, said apparatus consisting of a back and forth moving suction conveying element and a pair of intake rollers arranged downstream in transporting direction. For an operationally safe separating out of the book covers, it is proposed that the suction conveying element be raised slightly above the stacking table during the operating stroke and that it be lowered slightly below the stacking table during the return stroke. As soon as the front of the lowest book cover reaches the intake rollers, the upper roller which is not driven is lowered with the aid of working cylinders toward the lower, driven roller while the suction conveying element changes to its return stroke. Even though the use of the intake roller pair permits a secure conveying out of the separated out book covers, the speed conditions are unfavorable during the transfer of the separated book covers from the suction conveying element to the intake roller pair. Whereas the driven intake roller has a constant, high peripheral speed that is matched to the following conveyor, the suction conveying element near its turning point has long since moved past the maximum stroke speed.
During a renewed acceleration of the separated book cover in the intake roller pair, this results in abrasion and wear along the surface of the book cover which can result in a reduction in quality. Since only the lower roller of the intake roller pair is driven, a deformation as well as a slanted movement of the book covers should furthermore be expected which can lead to problems in the downstream-arranged units. Finally, the separating out capacity is also limited with this solution because of the fact that the upper intake roller is lowered onto the lower intake roller when the book cover arrives.
The European patent document EP 0384979B1 discloses an apparatus for separating out stacked book blocks, said apparatus having an endlessly circulating conveying line that is equipped with ejection elements as an alternative to a back and forth moving push table. While this apparatus causes hardly any vibrations, owing to the continuous movement of the conveying line, a quick interruption of the separating operation is not possible because of the ejection elements which are arranged at fixed distances to each other, thereby resulting in a disadvantage for the feeding of downstream-arranged apparatuses.
The German patent document DE 10223350A1 discloses an apparatus for separating printed sheets from a stack which apparatus essentially comprises support bars, a delivery device provided with pushing elements and a removal device provided with a pair of withdrawing rollers. The pushing elements in this case are driven by a linear motor that is assigned directly to the pushing device. As a result, the movement profile of the pushing device can be varied in dependence on the required removal speed. In addition, the linear motor offers the option for a direct adaptation of the pushing stroke to the format size of the printed sheet, thus reducing the number of necessary format changeovers. The apparatus can be operated such that the printed sheets are conveyed out either with a constant, pre-defined division or format-dependent with defined gaps between the printed sheets. The lowest printed sheet is accelerated with the aid of the pushing elements to the ejection speed and is then conveyed out with a constant speed by the downstream arranged pair of withdrawing rollers.
While this solution permits an extremely flexible separating out of printed sheets, the high costs and the high heat that is generated in the linear motor present a disadvantage. Since the primary part of the linear motor moves along with the pushing element, the motor must be fed via a drag chain which is problematic for a continuous operation with high accelerations. The relatively large mass to be accelerated furthermore results in high forces which must be absorbed by the frame for the apparatus. Depending on the separation rate, this can lead to high vibrations. The withdrawing roller pair with a fixed adjustment, relative to each other, is furthermore not suitable for processing adhesive-bound catalogs with a bulky back. Finally, there is the danger of the remaining stack tilting to one side during the separating out of the lowest printed sheet.
A problem with known approaches for a solution is that the movement sequences for the pushing process are fixedly predetermined and that the acceleration of the printed products consequently cannot be optimized for a high rate of separation. In addition, the speed conditions at the transfer points, especially during the product transfer from the push table to the removal rollers, may be unfavorable to such a degree that the quality of the printed products may suffer.
Owing to rigid movement sequences predetermined by the mechanical system, the movement may not be adapted to the respective format of the printed products to be separated out. The uncontrolled subsequent sliding of the remaining stack may lead to further problems, such as the printed products becoming wedged in the hopper chute, thus not permitting a safe separation process. Solution approaches which may permit a more flexible definition of the movement sequence between the push table and the conveying out speed may require more cost-intensive drive systems with a feed and control guidance that moves along. However, these systems may not be suitable for a continuous operation at a high production rate, for example at a rate of more than 15,000 operating cycles per hour.